feat: scienting-math/1 sources and derived/math.jsonl; lode references; stress fixes

Math content may say its source is in scienting-math/1's canonical TeX (form,
in no hash); derived/math.jsonl holds papermath's tree, symbols and issues,
and the validator now checks derived files. A symbol annotation names its
symbol by key; lode claim references use lode's tag and pin syntax. The zip
reader refuses entries zipfile cannot read, and checkpoint lines end in LF only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017R7sgDNvUGWY2zFPCq2JH6

fixtures/records/layer/layer.json

@@ -1 +1 @@
-{"@context":["http://www.w3.org/ns/anno.jsonld","https://paperspec.scient.ing/context/scienting-1.jsonld"],"audience":"student","created":"2026-10-11T19:00:00Z","creator":{"id":"tag:scient.ing,2026:key:ana","name":"Ana Example","type":"Person"},"docs":["smithlab/hale2026harmonic-damb"],"format":"scienting-layer/1","id":"tag:scient.ing,2026:layer:smithlab/kp4m2x7q","label":"Smith lab reading of Hale and Osei","license":{"spdx":"CC-BY-4.0"},"project":"smithlab-charges","purpose":"Glosses, claim links and exercises for new students.","total":11,"type":"AnnotationCollection","visibility":"team"}
+{"@context":["http://www.w3.org/ns/anno.jsonld","https://paperspec.scient.ing/context/scienting-1.jsonld"],"audience":"student","created":"2026-10-11T19:00:00Z","creator":{"id":"tag:scient.ing,2026:key:ana","name":"Ana Example","type":"Person"},"docs":["smithlab/hale2026harmonic-damb"],"format":"scienting-layer/1","id":"tag:scient.ing,2026:layer:smithlab/kp4m2x7q","label":"Smith lab reading of Hale and Osei","license":{"spdx":"CC-BY-4.0"},"project":"smithlab-charges","purpose":"Glosses, claim links and exercises for new students.","total":12,"type":"AnnotationCollection","visibility":"team"}